1. Field of the Invention
This invention relates to delustered regenerated cellulosic fibers and has particular, but not necessarily exclusive, reference to delustered regenerated cellulosic viscose rayon fiber.
2. Description of the Related Art
Regenerated cellulosic material may be produced by the well-known viscose rayon process which is described, for example, in the book "Man Made Fibers" by R.W. Moncrieff published by Heywood Books, London, England, Fifth edition 1970, pages 152 to 207. The term "viscose rayon" is also used herein to cover high tenacity cellulosic fibers, such as Modal fibers, and polynosic rayons, see Moncrieff pages 252 to 277. The contents of the two portions of the Moncrieff book are incorporated herein by way of reference.
More recently there has been commercialization.
In the viscose rayon fiber process as is described in Moncrieff a compound of cellulose --cellulose xanthate -- is produced in an alkaline solution. The cellulose xanthate solution is then spun or extruded through a suitable jet into a regeneration bath to form filaments. Typically the regeneration bath contains sulphuric acid and other additives. In the regeneration bath the cellulose xanthate is converted into cellulose filaments. These filaments are cut to form staple fiber. Staple fibre is typically produced from jets with large numbers (tens of thousand or more) of individual holes.
More recently processes have been evaluated whereby cellulose is taken into a true solution in a solvent, such as an aqueous N-methyl morpholine-N-oxide and the solution of cellulose forms a dope which is extruded through a suitable jet into a spin bath, where the solvent is leached out to regenerate the cellulosic material. An example of such fiber is the recently available cellulose fiber which has been given the generic name lyocell by BISFA (The International Bureau for the Standization of Man-Made Fibres).
Although the viscose rayon production process is extremely well known and no further explanation need be provided of the process as such, the cellulose solution process is more recent. A suitable process for the production of lyocell cellulosic fiber is described in U.S. Pat. No. 4,416,698, the contents of which are incorporated herein by way of reference.
In many cases it is desirable to produce regenerated cellulose fiber which has a delustered appearance. Conventionally, such a delustered appearance has been provided by the incorporation of titanium dioxide into the dope to be spun to produce the fiber (see Moncrieff page 162). Titanium dioxide is an inert pigment which delusters the fiber very satisfactorily. Unfortunately, however, the production of titanium dioxide gives rise to potential pollution problems. Titanium dioxide is very abrasive and, further, may catalyze photodegradation of cellulose. This abrasiveness can lead to considerable wear in the manufacturing plant used to produce the regenerated cellulosic fiber and also in the plant used to process the fiber. In such circumstances, the titanium dioxide incorporated into the fiber acts as an abrasive or polish, abrading the equipment used to process the fiber. The disadvantages of titanium dioxide as well as the advantages, are described in Moncrieff pages 698 to 699, the contents of which are incorporated herein by reference.
Although there are problems with the use of titanium dioxide as a delustrant, on balance the benefits of the use of titanium dioxide are such that it is the most frequently used commercial delustrant, as far as the applicants are aware.
Numerous other materials have been proposed as delustrants for regenerated celluloses.
In U.S. Pat. No. 3,833,021 there is disclosed the use of droplets of colloidal size to act as a delustrant not for fibers but for regenerated cellulose sausage casings. In the description of the prior art in U.S. Pat. No. 3,833,021 there is an extensive summary of the delustrants which have been used previously in regenerated cellulose products. Thus U.S. Pat. No. 3,833,021 refers to the following earlier references; U.S. Pat. No. 1,951,094, said to disclose the use of metal soaps and emulsions; U.S. Pat. No. 1,822,416, said to disclose the use of ground cellulose particles; U.S. Pat. No. 2,034,771, said to disclose the incorporation of sulphur particles; U.S. Pat. No. 2,077,700, said to disclose the use of chlorinated organic materials; U.S. Pat. No. 2,021,863, said to disclose the use of various thiocarbonic esters; U.S. Pat. No. 2,227,495, said to disclose the use of turpines and turpene ethers; U.S. Pat. No. 1,922,952, said to disclose the incorporation of mineral oil and sulphonated oil; U.S. Pat. No. 1,902,529, said to disclose the use of waxes in viscose; U.S. Pat. No. 2,057,323, said to disclose the use of proteins; U.S. Pat. No. 3,042,702, said to disclose the use of silicate esters; U.S. Pat. No. 2,334,358, said to disclose the use of titanium oxide pigments; U.S. Pat. No. 1,819,241, said to disclose the use of wax in oil; U.S. Pat. No. 2,081,847, said to disclose the use of delustring agents in a volatile organic solvent, and U.S. Pat. No. 2,166,741, said to disclose the introduction of delustring agents in volatile organic solvents.
Other delustrants have been proposed as is described in Moncrieff page 698. In GB-A-2008126 there is disclosed the use of styrene polymers, preferably polystyrene. Fibers have also been produced from dope containing Na.sub.2 CO.sub.3, which in turn results in gas evolution from sodium carbonate during spinning.
In East German Patent Specification (DD) 201,308 zinc compounds are added to provide a delustring effect. Zinc salts are also used to deluster synthetic fibers in accordance with the teachings of JP-A-48073600. In accordance with the teachings of JP-A-48006010 N-hexane-carbon tetrachloride has been used as a delustrant.
GB-A-1088012 describes the incorporation of opalescent particles or droplets in the extruded material to deluster films and filaments. U.S. Pat. No. 3,607,328 contains essentially the same text as U.S. Pat. No. 3,833,021 referred to above. In the official search on GB-A-2008126, the following references were cited GB-A-645954, GB-A-346793 and U.S. Pat. No. 4,007,248.
U.S. Pat. No. 3,899,452 describes a non-fibrous cellulosic film having enhanced rigidity obtained by the incorporation of from 1% to 25% of rigid hollow microspheres. GB-A-1387265 describes ion exchange celluloses particularly for ion exchange of large molecules, and refers to the incorporation of viscose solution into large diameter ( 1/4 inch-6.4 mm) balls.
It can be seen from the above than extensive investigations have been made over many years to develop delustrants for cellulosic fibers. As mentioned above, however, none has really taken the place of titanium dioxide, which for all its problems, particularly those associated with the abrasive nature of the material, its adverse effect on the quality of dyeing and its adverse effect on photodegradation has proved to be the most satisfactory delustrant commercially.
It has now been discovered, however, that an alternative material to titanium dioxide may be used as delustrant for regenerated cellulosic fibers which has been found to give not only satisfactory properties in terms of the delustring of the cellulose fibers, without suffering from the disadvantages of the abrasive nature of titanium dioxide, but also improved photodegradation characteristics, a cleaner color to dyed delustered fibers when compared to titanium dioxide delustered fiber and a crisper dryer "hand" to fabric produced from such fiber.